Optical brightener and what it really is

Short answer: Optical white is not a colour but a substance that absorbs invisible light and sends it out again as blue. The eye reads it as extra white, which is why some detergents give a whiter result.

Light gets converted

Optical brighteners absorb ultraviolet light and give it off as visible blue light. The extra blue tone makes yellow disappear, and the fabric looks whiter. It is an optical effect, not a change in the fabric's own colour, so it cannot be seen when the light is missing.

It only works in daylight

Ultraviolet light exists in sunlight but hardly in ordinary lamps. That is why optical white clothes look whitest outdoors. Indoors under a warm bulb the effect is almost gone. See bamboo hoodie dresses. A piece can look brilliant in the street and quite ordinary at home.

It wears off

The brightener sits on the surface and is gradually rinsed out. If the detergent has no optical white, the fabric slowly turns more yellowish. That is a normal development and not a sign that something went wrong. White clothes that have lost the layer can look muted even when clean.

Why yellow appears first

Natural fibres and skin oil give a faint yellowish tone that the eye sees as slightly dirty. Optical white covers that tone with blue light. Remove the brightener and the underlying tone shows. It is not damage, but the natural colour that was there all along.

Not the same as bleaching

Bleaching removes colour through a chemical reaction, while optical white adds a blue tone instead. The two work differently and serve different purposes. A bleach makes the fabric lighter, whereas a brightener tricks the eye into seeing it whiter. See bamboo T-shirt for women.

Disco light and black light

Under UV light, as found in nightclubs, clothes with optical white glow blue. That is because the light contains a lot of ultraviolet and the brightener turns it into visible blue. It is a neat way to see that the brightener works and stays in the fabric, even after a fresh wash.

Can it be avoided

Yes, by choosing detergents without optical white. Clothes then stay more naturally white, without the cool blue tone, and the colours change less over time. Detergents for coloured laundry often leave the brightener out, because colours are not meant to change. Check the ingredients on the pack.

Detergent for white and coloured

Detergent for whites often contains optical white, while detergent for colours mostly does not. So do not use white detergent on coloured clothes, since it can give a bluish or cold tone. Pick the one that suits the garment and read what the pack says. See bestsellers for women.

What to take away

Clothes are best judged in daylight, and that includes comparing shades of white. A piece that looks very white in a shop can look more muted at home. Know the difference and choose what you like wearing every day, rather than what looks strongest in one light.